The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An internal combustion engine (ICE) typically includes an oil circulating system. The oil circulating system includes an oil pump that is mechanically connected to a crankshaft of the ICE. This connection assures that the oil pump is circulating oil to and from components of the ICE when the crankshaft is rotating (i.e., engine is operating). Output flow of the oil pump is directly related to the rotating speed of the crankshaft. As the speed of the crankshaft increases, the output flow of the oil pump increases. This general increases oil pressure and provides increased lubrication of the ICE at increased engine speeds.
An engine oil pump introduces drag on an ICE due at least to the mechanical connection on the crankshaft of the ICE. The drag on the crankshaft increases with increased engine speed. Increased drag negatively affects available output torque and fuel economy of the ICE.
An engine oil pump is designed to provide a required flow (i.e., the amount of fluid that flows in a predetermined period) and pressure to adequately lubricate an ICE. The flow and pressure capabilities of the engine oil pump are based on worst case operating conditions. An example of a worst case operating condition is when engine oil is hot (e.g., 250 degrees Fahrenheit (° F.) to 300° F.) and the ICE is operating at high engine speeds (e.g., greater than 3000 revolutions per minute (rpm)).
For this reason, the engine oil pump provides oil flows and pressures that exceed required oil flows and pressures for certain operating states of the ICE. As a non-worst case operating state example, an ICE may have a cool oil temperature (e.g., less than 250° F.) and be operating at a low engine speed. In this operating state, the engine oil pump may provide flow and pressure for the worst case operating condition, which is greater than that required. As a result, unjustified drag on the crankshaft occurs during non-worst case operating states. This decreases available output torque and fuel economy of the ICE.